Although there has been a revived interest in the possible therapeutic effects of hallucinogens (Griffiths et al. 2006;Nichols 2004), such drugs are also popular drugs of abuse. Hallucinogens are generally considered to be physiologically safe (i.e., they do not result in physiological dependence nor do they cause disruption in cardiovascular, renal or hepatic functions) (Nichols 2004;O'Brien 2001). However, users of hallucinogens can experience hallucinogen persisting perception disorder (HPPD), fatal accidents resulting from distorted perceptions (e.g., attempting to fly), and psychoses-like side effects such as changes in cognitive functions and depersonalization (Abraham and Duffy 2001;Nichols 2004). In addition, use of hallucinogens may initiate the onset of psychosis or depression (Cohen 1960;Nichols 2004). The intravenous (IV) drug self-administration model has been used extensively to characterize the reinforcing effects of psychoactive compounds (Panlilio and Goldberg 2007). However, it has been generally accepted by the scientific community that while humans use LSD recreationally, laboratory animals do not self-administer it. The notion that laboratory animals don't self-administer LSD is likely based on data collected in the German lab of F. Hoffmeister in the 1970's, though the data was never published (Johanson and Balster 1978). Indeed, there are no peer-reviewed studies reporting the procedures used, nor the negative results of attempts to establish LSD as a reinforcer in laboratory animals. Accordingly, the conventional wisdom that hallucinogens do not function as reinforcers in laboratory animals is currently being reexamined. Fantegrossi and colleagues reported low levels of self-administration of the prototypical hallucinogens mescaline and psilocybin in rhesus monkeys (Fantegrossi et al. 2004). LSD also produces conditioned place preference in male rats (Meehan and Schechter 1998;Parker 1996). Thus, given that LSD is a popular drug of abuse, there are no published accounts of attempts to establish IV LSD as a reinforcer, LSD produces conditioned place preference in male rats (Meehan and Schechter 1998;Parker 1996), and other prototypical hallucinogens (i.e., mescaline and psilocybin) function as IV reinforcers in rhesus monkeys (Fantegrossi et al. 2004), we propose to examine the reinforcing effects of LSD using an IV self-administration model in baboons (a species with phylogenetic proximity to humans). PUBLIC HEALTH RELEVANCE: Although there has been a revived interest in the possible therapeutic effects of hallucinogens, such drugs are also popular drugs of abuse with the potential for adverse effects. An examination of the reinforcing effects of LSD in baboons is clinically relevant to the therapeutic use of these compounds, as well as the potential treatment for the abuse of these compounds.